Silicate Coatings

ABSTRACT

Metal products having improved properties and processes for preparing the metal products are provided. The present disclosure provides for a metal product comprising a metal surface, an oxide layer and a glass layer. The glass layer is provided by coating a stable aqueous silicate or borosilicate solution onto the metal surface and curing the aqueous solution to produce a glass layer. The metal products have surface characteristics that outperform all anodized metal surfaces.

CROSS-REFERENCE TO RELATED APPLICATION

This disclosure claims the benefit of priority to U.S. patentapplication Ser. No. 14/656,802, filed Mar. 13, 2015, which claimspriority to Provisional Patent Application No. 62/047,280, filed 8 Sep.2014, the disclosures of which are incorporated herein in theirentirety.

FIELD OF THE INVENTION

The herein disclosed invention is directed to protective inorganiccoatings for aluminum and aluminum oxides.

BACKGROUND

The electrochemical formation of oxide layers on aluminum is awell-known and widely used industrial procedure to produce protectiveand/or decorative coatings on aluminum and/or aluminum alloys.Electrolytically produced aluminum oxide layers protect the base metalfrom corrosion and weathering and furthermore may increase the surfacehardness and the abrasive resistance of the aluminum part.

Many different processes of anodizing are known. For example, aluminummaterials can be anodized in electrolytes such as sulfuric acid, chromicacid, phosphoric acid, and oxalic acid by the application of AC or DCcurrents at a bath temperature of 10-25° C. Variations in this treatmentcan change the thicknesses and/or hardness of the anodized aluminumoxide layer.

The porosity of the anodized layer may be favorable for the adhesion oforganic coatings, but exhibits a major drawback, namely the lack ofprotection against corrosive media. Therefore, and to impart maximumcorrosion stability, anodized aluminum layers are often sealed in asubsequent process step. During sealing, which might be a hot sealingand/or cold sealing process, the aluminum oxide becomes hydrated and istransformed from its amorphous, essentially water-free constitution to aboehmite structure. This transformation is accompanied by a volumeexpansion or swelling of the oxide that in turn procures the sealing ofthe porous structure. Hot sealing of the anodized layer is usuallyperformed in hot water or in steam, whereas the cold sealing process isoperated at temperatures close to 30° C. in the presence of nickelfluoride. Sealing improves the corrosion resistance and resistance toweathering of anodized aluminum parts in a pH range from 5-8.

Unfortunately, sealed anodized aluminum surfaces continue to displaypoor corrosion resistance and stability below pH 4 and/or above pH 9.Additional seals or coatings have been attempted but improved coatingswith stability to high and low pH, accelerated corrosion testing,abrasion, and fogging are needed.

SUMMARY

Herein is disclosed a layered product that includes an aluminum oxidelayer having a composition that is free of silicates; and a silicateglass layer directly carried by the aluminum oxide layer and having asilicate glass layer EDX composition that consists of silicon, oxygen,sodium, optionally lithium, and optionally boron; wherein the silicateglass layer EDX composition is free of aluminum.

Additionally disclosed is a process for preparing a surface coating thatincludes forming a coated-aluminum-oxide layer by applying an aqueoussilicate solution to an aluminum oxide layer having a thickness of about1 μm to about 25 μm, the aluminum oxide layer consisting of a sealed,anodized-aluminum layer or a hydrated PVD alumina layer, the aqueoussilicate solution having a pH of about 11 to about 13, a compositionthat includes a ratio of SiO₂ to M₂O of about 3.5 to about 2, where M isselected from Li, Na, K, and a mixture thereof, and a ratio of SiO₂ toB₂O₃ of about 10:1 to about 200:1; and thereafter, polymerizing andcuring a silicate glass on the sealed, anodized-aluminum layer by (A)heating the coated, anodized-aluminum layer to a temperature of about200° C. to about 500° C. or (B) exposing the coated, anodized-aluminumlayer to an infrared source.

BRIEF DESCRIPTION OF THE FIGURES

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and accompanying drawingfigures wherein:

FIG. 1 is a plot of the average atomic percentages of silicon andaluminum as a function of distance from the surface of a comparativeproduct as calculated from EDX;

FIG. 2 is a plot of the average atomic percentages of silicon andaluminum as a function of distance from the surface of aherein-described product as calculated from EDX;

FIG. 3 is a comparison between silicon atomic percentages in thealuminum oxide layer of a comparative sample (FIG. 1) and aherein-described product (FIG. 2);

FIG. 4 is a plot of ion counts as a function of distance as determinedby TOF-SIMS for a comparative product, where milling began at thesurface (T=0);

FIG. 5 is a plot of ion counts as a function of distance as determinedby TOF-SIMS for a herein-described sample, where milling began at thesurface (T=0);

FIG. 6 is a photograph of a comparative product (prior art sample)(bottom) and a herein-described sample (top) after a 24 h CASS test;

FIG. 7 is a photograph of a partially coated sample after heating to280° C. for 15 minutes, the photograph (Left) showing cracking and/orcrazing of an uncoated sealed anodized aluminum layer and (Right)showing the undamaged coated section.

While specific embodiments are illustrated in the figures, with theunderstanding that the disclosure is intended to be illustrative, theseembodiments are not intended to limit the invention described andillustrated herein.

DETAILED DESCRIPTION

The present disclosure is directed to processes for manufacturing and tometal products that demonstrate excellent durability and ease ofpreparation. In general, a product includes a metal or metal alloysubstrate, an oxide layer on the surface of the metal or metal alloysubstrate, and a glass layer on the oxide layer that is a silicate orborosilicate glass. The product according to this invention may be usedin interior/exterior applications such as architectural fixtures,automobile parts, aerospace parts, marine components, bicyclecomponents, motor bike parts, heavy transport vehicle parts (includingtruck, train, and rail), military related components, mirrors,streetscape components (e.g., street lights and exterior signs),furniture, appliances (e.g., refrigerators, washing machine, clothingdriers, dishwashers, range, table top appliances (e.g., mixers,blenders, toasters, rice makers)), solar power components (e.g.,reflectors, and collectors), consumer products and related parts (e.g.,cell phones, and computer components), heat exchanges, medicalinstruments and tools, and/or oil and gas production components (e.g.,coil tubing); wherein the substrate is generally considered the fixtureor part and the oxide layer and silicate glass coat the fixture or part.Architectural fixtures and parts include material for or items selectedfrom window frames, window trim, doors, claddings, mirrors, reflectors,lamp housings, hinges, handles, furniture parts including table or chairlegs, seats or tops, brackets, tracks, railings, and/or hardware.Automobile parts include members of vehicle bodies and/or vehiclewheels; including, for example, roof racks/rails, window trim, wastefinisher, step/side bars, door trim, lamp trim, door handles, exhaustmanifolds, reflectors, fuel cap flaps, spoilers, pillar covers, doorhandle anti-scratch plates, antenna, brandings/emblems, window visors,speaker trim, hub caps, wheel rims, lug nuts, engine parts (e.g.,pistons, blocks, shafts, cams, pulleys, housings, and covers), and/orexhaust parts (e.g., exhaust tubing/piping, mufflers, converter covers,clamps, hangers, and tail pipes). Aerospace parts include, for example,engine covers, panels, spinners, propellers, wings, flaps, elevators,and cowlings. Marine components include, for example, hulls, masts,booms, pulleys, winch, tiller, spreaders, grabrail, turnbuckle,stanchion, hatch trim, and/or trailers. Bicycle components include, forexample, frames, posts, tubes, handle bars, rims, levers, gears, and/orhubs. Motor bike parts include, for example, wheels, suspension tubes,swinging arms, engine parts, exhaust parts, and trim.

Herein is disclosed a layered product that includes an aluminum oxidelayer having a composition that is free of silicates, preferably havingan aluminum oxide layer EDX composition that is free of silicon, boron,and/or nickel; and a silicate glass layer directly carried by thealuminum oxide layer and having a silicate glass layer EDX compositionthat consists of silicon, oxygen, sodium, optionally lithium, andoptionally boron; wherein the silicate glass layer EDX composition isfree of aluminum. The silicate glass layer has a composition thatincludes about 55 wt. % to about 98 wt. % SiO₂, 0 wt. % to about 6.7 wt.% B₂O₃, and about 2.3 wt. % to about 36 wt. % M₂O, wherein M is selectedfrom the group consisting of lithium, sodium, potassium, and a mixturethereof; preferably wherein M is a mixture of Li and Na, for examplewith a Li:Na ratio of about 1:10 to 10:1; wherein the silicate glasslayer includes less than 0.1 wt. % aluminum, preferably less than 0.01wt. % aluminum, even more preferably less than 0.001 wt. % aluminum.Preferably, the silicate glass layer has a TOF-SIMS composition thatconsists of silicon, oxygen, sodium, optionally lithium, and optionallyboron; wherein silicate glass layer TOF-SIMS data may show a traceamount of aluminum. The silicate glass layer can have a thickness in therange of about 50 nm to about 3000 nm, about 50 nm to about 2000 nm,about 50 nm to about 1500 nm, about 100 nm to about 1500 nm, about 250nm to about 1500 nm, or about 500 nm to about 1000 nm.

The herein disclosed aluminum oxide layer is, preferably, free ofsilicates. That is, the aluminum oxide layer does not include glassforming silicone oxides (e.g., SiO₂), aluminosilicate, borosilicates, ormixtures thereof. In one instance, the aluminum oxide layer has an EDXcomposition that consists of aluminum, oxygen, sulfur, and an optionalcolorant; and/or a TOF-SIMS composition that consists of aluminum,oxygen, sulfur, and an optional colorant. Preferably, the aluminum oxidelayer TOF-SIMS composition is free of silicon.

In one instance, the aluminum oxide layer is a sealed aluminum oxidelayer or a PVD aluminum oxide layer (or hydrated PVD aluminum oxidelayer). In still another instance, the layered product includes analuminum surface; wherein the aluminum oxide layer is directly attachedto the aluminum surface. Preferably, the layered product still furtherincludes a substrate, carrying the aluminum oxide layer, selected fromthe group consisting of aluminum, an aluminum alloy, and stainlesssteel.

Preferably, the layered product is free of an aluminosilicate orsilicate/alumina interdiffusion. Even more preferably, the layeredproduct passes both a 2 minute “pH 14 Test” and a “24-hour CASS Test”.

Further disclosed is a coated product that includes an aluminum surfacedirectly attached to a barrier layer. This barrier layer is directlyattached to an aluminum oxide layer which is directly attached to asilicate glass layer. Herein, “directly attached” signifies and meansthat the denoted layers are chemically and/or physically bonded withoutan intervening layer. This absence of an intervening layer can bedetermined by spectroscopic and/or microscopic methods, for example,energy-dispersive X-ray (EDX) spectroscopy, time-of-flight secondary ionmass spectroscopy (TOF-SIMS), and/or scanning electron microscopy (SEM).Still further disclosed is a corrosion resistant coating that includesan aluminum oxide layer attached to a substrate, where the aluminumoxide layer can have a composition that includes, for example, about 70wt. % to about 90 wt. % Al₂O₃, about 2.5 wt. % to about 7.5 wt. % H₂O,and about 10 wt. % to about 20 wt. % SO₃. The corrosion resistantcoating can include a borosilicate glass directly attached to thealuminum oxide layer, wherein the borosilicate glass has a compositionthat includes SiO₂, B₂O₃, and M₂O. M₂O is an alkali metal oxide where Mis selected from the group consisting of Li, Na, K, and a mixturethereof (e.g., Na₂O, Li₂O, LiNaO, K₂O). Notably, the components of theborosilicate glass (SiO₂, B₂O₃, and M₂O) are not distinct but are partof and, preferably, homogeneously distributed throughout the glass. Thatis, the silicate glass layer and the aluminum oxide layer compositionsare described based on recognizable components (e.g., SiO₂, B₂O₃, Al₂O₃)in the layers but consists of or comprise homogeneous compositions.

The composition of the silicate glass layer, based on the materials usedto prepare the layer, can include about 55 wt. % to about 98 wt. % SiO₂,0 wt. % to about 6.7 wt. % B₂O₃, and about 2.3 wt. % to about 36 wt. %M₂O. Notably, M is selected from the group consisting of lithium,sodium, potassium, and a mixture thereof and this selection cansignificantly affect the weight percentages of the component parts. Forexample in a composition wherein the molar ratio of the components areheld constant, the variation of M₂O from one hundred percent lithium,with an atomic mass of 6.941, to one hundred percent potassium, with anatomic mass of 39.098, causes a ten-fold change in the weightpercentages. A preferably description of the composition of the silicateglass layer is based on molar ratios of the components, yet such adescription is not common in the art. Preferably, the molar ratios ofthe components (expressed as percentages) are about 67% to about 81%SiO₂, 0% to about 7% B₂O₃, and about 17% to about 28% M₂O.Alternatively, the molar ratios can be about 75% to about 80% SiO₂, andabout 20% to about 25% M₂O; or about 67% to about 76% SiO₂, about 3% toabout 5% B₂O₃, and about 19% to about 30% M₂O.

The silicate glass layer can have an “EDX composition” which is thesilicate glass layer composition as determined by EDX spectroscopy (seeFIG. 2). Preferably, the silicate glass layer EDX composition includessilicon, oxygen and sodium. More preferably, the silicate glass layerEDX composition consists of silicon, oxygen, and elements selected fromthe group consisting of sodium, lithium, potassium, boron, and mixturesthereof. In various aspects, the silicate glass layer EDX compositioncan consist of silicon, oxygen, sodium, and boron; silicon, oxygen,lithium, and boron; silicon, oxygen, sodium, and lithium; silicon,oxygen, sodium, lithium, and boron; or silicon, oxygen, sodium, lithium,potassium, and boron. In examples where the silicate glass composition(as determined by EDX or other methods) includes boron, the silicateglass is also described as a borosilicate glass. The silicate glasslayer EDX composition can further be described as consisting of silicon,oxygen, sodium, optionally lithium, and optionally boron. In someaspects, the silicate glass layer may be described as consisting ofsilicon, oxygen, optionally boron, sodium, and optionally lithium butmay include trace amounts of potassium due to materials employed for theproduction of the silicate glass layer having slight impurities.Notably, the silicate glass layer may in fact include hydrogen buthydrogen is not observable by EDX spectroscopy. More preferably, thesilicate glass layer EDX composition is free of aluminum.

The silicate glass layer can have a “TOF-SIMS composition” which is thesilicate glass layer composition as determined by TOF-SIMS (see FIG. 5).Preferably, the silicate glass layer TOF-SIMS composition includessilicon, oxygen, and sodium. More preferably, the silicate glass layerTOF-SIMS composition consists of silicon, oxygen and elements selectedfrom the group consisting of sodium, lithium, potassium, boron, andmixtures thereof. Notably, the silicate glass layer may include hydrogenbut is not determined due to experimental difficulties and samplepreparation variations. Additionally and due to the extremely highsensitivity of TOF-SIMS, the silicate glass layer TOF-SIMS compositionmay appear to include trace amounts of aluminum. Preferably, thesilicate glass layer includes less than 0.1 wt. % aluminum, preferablyless than 0.01 wt. % aluminum, even more preferably less than 0.001 wt.% aluminum.

When the silicate glass layer includes both sodium and lithium, thesilicate glass layer has a Na:Li atom ratio that is preferably about 1:9to about 9:1. More preferably, the Na:Li atom ratio is about 1:5 toabout 5:1; even more preferably, about 1:2.5 to about 2.5:1.

When the silicate glass layer is a borosilicate glass layer, that iswhen the silicate glass layer includes boron, the silicate glass layerhas a Si/B atom ratio that is, preferably, about 10:1 to about 200:1.More preferably, the Si/B ratio is about 10:1 to about 100:1; even morepreferably about 25:1 to about 100:1.

The silicate glass layer can have a thickness of about 100 nm, 200 nm,300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1500nm, 2000 nm, 2500 nm, or 3000 nm. Alternatively, the silicate glasslayer thickness can be in the range of about 50 nm to about 3000 nm,about 50 nm to about 2000 nm, about 50 nm to about 1500 nm, about 100 nmto about 1500 nm, about 250 nm to about 1500 nm, or about 500 nm toabout 1000 nm.

In another example, the silicate glass layer includes a mixture ofalkali metals selected from a mixture of sodium and potassium; sodium,lithium and potassium; and lithium and potassium. That is, in thisexample the silicate glass layer includes a mixture of alkali metalswherein one alkali metal is potassium. Preferably, the silicate glasslayer includes a non-homogenous distribution of potassium. For example,wherein the silicate glass layer includes a high-potassium region nearthe surface (away from the aluminum oxide layer), as compared to alower-potassium concentration in a region of the silicate glass adjacentto the substrate. That is, the silicate glass can include a plurality ofregions as differentiated by the depth profile of the potassiumconcentration.

Preferably, the concentration of the silicon in the silicate glass layeris consistent across and through the layer. The consistency of thecomposition can be determined from the silicon concentration in thesilicate glass layer EDX composition, preferably the siliconconcentration varies by less than 5%, 4%, 3%, 2%, or 1% across andthrough the silicon glass layer. Additionally, the concentration ofoxygen in the silicate glass layer is, preferably, consistent across andthrough the layer. That is, the oxygen concentration in the silicateglass layer EDX composition, preferably, varies by less than 5%, 4%, 3%,2%, or 1% across and through the silicate glass layer.

The silicate glass layer is preferably a dense, impermeable layer. Morepreferably, the silicate glass layer is non-porous. Even morepreferably, the silicate glass layer is a transparent, amorphous solid.

As described above, the aluminum oxide layer can include about 70 wt. %to about 90 wt. % Al₂O₃, about 2.5 wt. % to about 7.5 wt. % H₂O, andabout 10 wt. % to about 20 wt. % SO₃; about 75 wt. % to about 85 wt. %Al₂O₃, about 3.5 wt. % to about 5.5 wt. % H₂O, and about 12.5 wt. % toabout 17.5 wt. % SO₃; or about 80-81 wt. % Al₂O₃, about 5-6 wt. % H₂O,and 14-15 wt. % SO₃. In alternative examples, the aluminum oxide layercan be free of SO₃. In one particularly preferable example, the aluminumoxide layer has an EDX composition that consists of aluminum, oxygen,sulfur, and an optional colorant. Even more preferably, the aluminumoxide layer EDX composition is free of silicon, the aluminum oxide layerEDX composition is free of nickel, the aluminum oxide layer EDXcomposition is free of silicon and nickel, and/or the aluminum oxidelayer EDX composition is free of silicon, boron, and nickel.

Preferably, the composition of the aluminum oxide layer is consistentacross and through the layer. The consistency of the composition can bedetermined from the aluminum concentration in the aluminum oxide layerEDX composition, preferably the aluminum concentration varies by lessthan 5%, 4%, 3%, 2%, or 1% across and through the aluminum oxide layer.The consistency of the composition can also be determined from theoxygen concentration in the aluminum oxide layer EDX composition,preferably the oxygen concentration varies by less than 5%, 4%, 3%, 2%,or 1% across and through the aluminum oxide layer. In examples wherein adye is added to the aluminum oxide layer during manufacturing, thecomposition may vary through the layer depth due to localization of thedye in aluminum oxide pores.

The aluminum oxide layer EDX composition can include or, preferably,consists of 31-36% aluminum, 60-70% oxygen, and 2-5% sulfur; morepreferably, 31-35% aluminum, 63-67% oxygen, and 3-4% sulfur; and evenmore preferably, 32-34% aluminum, 64-66% oxygen, and 3-3.5% sulfur. Asdescribed above, hydrogen concentrations are not available from EDXspectroscopy and therefore are not part of the EDX composition.Additionally, the aluminum oxide layer EDX composition can include analuminum:oxygen ratio of about 1:2.

The aluminum oxide layer TOF-SIMS composition includes aluminum andoxygen. In one example, the aluminum oxide layer TOF-SIMS compositionincludes or, preferably, consists of aluminum, oxygen, sulfur, and anoptional colorant. More preferably, the aluminum oxide layer TOF-SIMScomposition is free of silicon, or free of silicon and boron (see FIG.5). In some examples, the aluminum oxide layer TOF-SIMS compositionincludes sodium and/or lithium but, preferably, is substantially freeof, or is free of, potassium. Notably, experimental conditions may makethe observation of one or more atoms in the TOF-SIMS analysis difficultto identify—for example, the O+ mass/ion was infrequently observed at 16amu but readily observable as the Cs ion pair, CsO+, a result of Cs ionmilling.

The aluminum oxide layer can have a thickness of less than about 50microns, 40 microns, 30 microns, 25 microns, 20 microns, 10 microns, 5microns, 4 microns, 3 microns, 2 microns, 1 micron, or 500 nm.Preferably, the aluminum oxide thickness is a range of about 1 to about30 microns, about 2 to about 25 microns, about 3 to about 20 microns, orabout 5 to about 25 microns. In one particular example, the aluminumoxide layer has a thickness less than about 10 microns and theborosilicate glass has a thickness less than about 1 micron.

The aluminum oxide layer can include a boehmite/bayerite region withoutdeviating from the compositional ranges provided above. Notably, theboehmite/bayerite region includes a hydrated aluminum oxide, that is, analuminum oxide with a higher proportion of hydroxyl groups than adehydrated Al₂O₃. For example, the boehmite/bayerite region includesAlO(OH) and/or Al(OH)₃ groups. In examples with the boehmite/bayeriteregion, the boehmite/bayerite region is directly attached to thesilicate glass layer. In one example, the boehmite/bayerite region iswithin the aluminum oxide layer, with a higher proportion of hydroxylgroups, and is positioned between a region with a lower proportion ofhydroxyl groups and the silicate glass layer. In another example, theboehmite/bayerite region extends through the entire aluminum oxidelayer. The boehmite/bayerite region may be identified in TOF-SIMS plotsof aluminum counts over time (depth) (see FIG. 5). Without being boundto theory, variation in aluminum counts at or near the silicate glasslayer can be due to an increased friability of the boehmite/bayeriteregion compared to the majority of the aluminum oxide layer. Thisvariation, as shown in FIG. 5 as seen between milling times of about1300 and 2000, is believed to be or is indicative of theboehmite/bayerite region.

As noted above, this composition can include a barrier layer directlyattached to the aluminum oxide layer. Preferably, the barrier layer hasa TOF-SIMS composition that includes aluminum and oxygen. In someexamples, the barrier layer TOF-SIMS composition further includes sodiumand/or lithium. In still further examples, the barrier layer TOF-SIMScomposition may include trace amounts of silicon. Notably, a friabilityof the barrier layer imparts a sharp increase in the number of counts inthe TOF-SIMS analysis.

Preferably, the compositions include an aluminum surface carried by asubstrate. The substrate can be composed of, for example, aluminum, analuminum alloy, or stainless steel. The aluminum alloy can be selectedfrom the series consisting of a 1000 series alloy, a 2000 series alloy,a 3000 series alloy, a 4000 series alloy, a 5000 series alloy, a 6000series alloy, a 7000 series alloy, and a 8000 series alloy. In onepreferable example, the aluminum alloy is a 6000 series alloy; inanother preferable example, the aluminum alloy is a 3000 series alloy;in still another example the aluminum alloy is a 1000 series alloy. Thealuminum or aluminum alloy can be cast, extruded, hot rolled, coldrolled, annealed, or hardened. In one preferable instance, the aluminumor aluminum alloy is extruded. In another instance, the aluminum oraluminum alloy is rolled. In still another instance, the cast, extruded,or rolled aluminum or aluminum alloy is annealed. In yet anotherinstance, the cast, extruded, or rolled aluminum or aluminum alloy ishardened. In other examples the substrate can be, for example, stainlesssteel, a ceramic, or a plastic.

An important feature is an extraordinary resistance to corrosion and ordegradation provided by the herein described silicate glass coating.Generally, the resistance to corrosion or degradation is determined bythe performance of test samples in the following test methods. Therein,samples are evaluated on a “pass/fail” scale; typically, passing aspecific test was indicated by no change in visual appearance at theconclusion of the test whereas failure of a specific test was indicatedby significant corrosion or degradation of the sample. Some testsprovided less binary results; in these circumstances samples wereadditionally graded on a “−/0/+” scale: where “−” equates to failure,“0” equates with a minor change in appearance (e.g., lightdiscoloration, spotting, or clouding over less than 10% of the coatedsurface area), and “+” equates with no change in visual appearance.Herein, samples that exhibit no visual change in appearance (score a“+”) are considered to have “excelled” at the test.

In a first instance, the herein described coating provides the coatedmaterials with resistance to acidic environments. That is, the coatedproduct passes and/or excels on a “pH 1 Test”. The “pH 1 Test” is a 10minute immersion in an aqueous 0.1 M HCl solution at ambient temperature(20-25° C.).

In a second instance, the herein described coating provides the coatedmaterials resistance to basic environments. That is, the coated productexcels on a “pH 13.5 Test”. The “pH 13.5 Test” is conducted at 25-30° C.by (a) 10 min immersion in pH 1 solution; (b) rinse in water and dry,(c) age at elevated temperature at 40° C. for 1 h, then without coolingdown (d) 10 min immersion in pH 13.5 solution, and (e) rinse in waterand dry. This test is commonly known as standard TL 182 (Volkswagen AG).

In another instance, the coated product passes and or excels on a 2minute “pH 14 Test”, more preferably a 10 minute “pH 14 Test”, or evenmore preferably a 30 minute “pH 14 Test”. The “pH 14 Test” is conductedby immersing the test sample in a 1 M aqueous NaOH solution at 70° C.(pH 14). The sample is held in the caustic solution for at least twominutes, thereafter removed and rinsed with water and dried. Typicalfailure under the pH 14 Test was a sheeting or delamination of acoating. Accordingly, samples were evaluated on a pass/fail basiswherein samples that exhibited a delamination or sheeting failed whereassamples that maintained their integrity passed. In limited samples, aslight opacity (clouding) was observed after completion of the test; inthese samples were considered to have passed the test. Preferably,samples exhibited no change (e.g., no clouding, no corrosion, no changein color) in visual appearance as a result of the pH 14 Test; thesesamples are considered to have “excelled” under the test conditions.

In yet another instance, the herein described coating provides thecoated materials with resistance to a Copper Accelerated Acetic AcidSalt Spray (CASS) Test (see FIG. 6). Preferably, the coated productpasses a “24-hour CASS Test”, a “48-hour CASS Test”, a “72-hour CASSTest”, and/or a “120 hour CASS Test”. The “CASS Test” is a knownindustry standard, e.g., ASTM B368-09. Typical failure under the CASSTest is pinhole corrosion. Accordingly, samples were evaluated on apass/fail basis, wherein samples that exhibited pinhole corrosion failedwhereas samples that maintained their integrity passed. In limitedsamples, slight changes in visual appearance were observed; thesesamples were considered to have passed the test. Preferably, samplesexhibited no change in visual appearance as a result of the CASS Test;these samples are considered to have “excelled” under the testconditions. Additionally, preferred samples exhibited no change invisual appearance as a result of an Extended CASS Test (48 hours).

In still yet another instance, the herein described coated productpasses a “Fogging Test.” The “Fogging Test” included subjecting thesample to nitric acid vapors in 95-100 percent humidity at about 38° C.for 72 hours.

A further failure test is an “abrasion test”. Herein, the abrasion testincluded 20 cycles (40 lengths) of polishing with a Grade 1 steel wool(medium; with a fiber width of 0.06 mm) at a force of 200 g/cm².Additional abrasion testing can be conducted, e.g., an “Amtec KistlerCar Was Test” and/or a “Taber Test”.

Further failure tests include a “Heat Resistance Test” (120 hours at200° C.), a Neutral Salt Spray Test (e.g., ASTM B117; 1,000 hours), anda “Humidity Test” (300 hours). Preferably, the herein described coatedproduct passed these test, individually and as a group.

Preferably, the herein described coated product passes a “pH 1 Test”;passes a “pH 13.5 Test”, passes a 2 minute “pH 14 Test” (preferably, a10 minute “pH 14 Test”, more preferably, a 30 minute “pH 14 Test”); andpasses a “24-hour CASS Test” (preferably, a “48-hour Cass Test”, a“72-hour CASS Test”, or a “240-hour CASS Test”).

In another embodiment, the coated product includes a substrate carryingan aluminum oxide layer that is directly attached to a silicate glasslayer. Here, the coated product can be free of a barrier layer, e.g.,the aluminum oxide layer can be directly attached to the substrate. Oneexample of an aluminum oxide layer directly attached to the substrate isphysical vapor deposited (PVD) aluminum oxide carried by a substrate,where a PVD aluminum oxide layer was formed directly on the receivingsubstrate. The composition of the aluminum oxide layer (e.g., the PVDaluminum oxide layer) can be free of sulfur. Preferably, the aluminumoxide layer composition can consist of aluminum and oxygen, and morepreferably, in a ratio of about 2:3 (e.g., Al₂O₃). In another example,the aluminum oxide layer composition can include aluminum, oxygen andhydrogen. Furthermore, the aluminum oxide layer (e.g., the PVD aluminumoxide layer) can include or consist of a bayerite/boehmite regionadjacent to the silicate glass layer.

Additionally disclosed is a process for preparing the above describedsurface coatings or coated products. Generally, the process includescoating an aluminum oxide with an aqueous silicate solution and thenpolymerizing and curing a silicate glass formed from the silicatesolution. An important feature of the process, alluded to above in thedescription of the surface coatings, is preventing silicate penetrationinto the aluminum oxide and preventing aluminum dissolution andappearance in the silicate glass. The control of the resultingcompositions provided by the herein disclosed process yields a coatingor coated product with unexpected and exceptional resistance tocorrosion and damage.

At a minimum, the process can include forming an aluminum oxide layercoated with an aqueous silicate solution and then polymerizing andcuring a silicate glass on the aluminum oxide layer. For a completeunderstanding, the process is herein described with additional,preferable, steps applicable for the formation of the above describedcoatings or coated products.

The herein disclosure includes a process for preparing surface coatingthat can include forming a coated-aluminum-oxide layer by applying anaqueous silicate solution to an aluminum oxide layer having a thicknessof about 1 μm to about 25 μm, the aluminum oxide layer consisting of asealed, anodized-aluminum layer or a hydrated PVD alumina layer, theaqueous silicate solution having a pH of about 11 to about 13, acomposition that includes a ratio of SiO₂ to M₂O of about 3.5 to about2, where M is selected from Li, Na, K, and a mixture thereof, and aratio of SiO₂ to B₂O₃ of about 10:1 to about 200:1; and thereafter,polymerizing and curing a silicate glass on the sealed,anodized-aluminum layer by (A) heating the coated, anodized-aluminumlayer to a temperature of about 200° C. to about 500° C. or (B) exposingthe coated, anodized-aluminum layer to an infrared source. The processcan further include providing an aluminum surface; anodizing thealuminum surface to provide an unsealed, anodized-aluminum layer; andthen hot sealing the unsealed aluminum oxide layer to provide a sealed,anodized-aluminum layer. The hot sealing can include a hot sealing timeof less than 6 min/micron and at least 5 min/micron, 4 min/micron, 3min/micron, 2 min/micron, 1 min/micron, 30 sec/micron, or 10 sec/micron;wherein forming the sealed, anodized aluminum layer from theunsealed-anodized-aluminum layer consists of the hot sealing process.

Still further, the process can includes a time between the conclusion ofthe hot sealing process and forming the coated, anodized-aluminum layerof less than 60, 45, 40, 35, 30, 25, 20, 15, 10 or 5 minutes.Preferably, the time is less than 5 minutes or is no more than theamount of time necessary to remove the sample from a hot sealing bath orapparatus, cool to about room temperature, and then immerse in theaqueous silicate solution (in practice, often less than 1 minute). Inanother instance, the sealed, anodized-aluminum layer may be held in awet atmosphere, in water, or coated with water; before forming thecoated, anodized-aluminum layer by applying the aqueous silicatesolution.

Further disclosed in a multistep process that includes a first step ofproviding an aluminum oxide layer. The aluminum oxide layer can beprepared by anodizing aluminum or an aluminum alloy or by deposition ofan aluminum oxide layer by, for example, physical vapor deposition(PVD). While chemically similar, the structures of the aluminum oxidelayers provided by different methods are distinct. Anodization providesa well-known porous layer whereas PVD, typically, provides a densenon-porous layer. Prior to coating with the silicate solution, thealuminum oxide layer is, preferably, non-porous and/or includes a highproportion of hydroxyl groups on an outer surface.

The aluminum oxide layer can be provided (e.g., by anodization or PVD)on an aluminum, aluminum alloy, or other surface. In examples where thealuminum oxide layer is provided on an aluminum or aluminum alloysurface, the surface, preferably, has a <110> or a <112> orientation. Inone particularly preferably instance, the aluminum or aluminum alloysurface has a <110> orientation. Notably, the aluminum or aluminum alloysurface is not single-crystalline and the surface orientation mayinclude other crystal orientations. Herein, an aluminum or aluminumalloy that is designated as having a <110> orientation may include<100>, <111>, <211>, and <311> orientations. Preferably, the aluminum oraluminum alloy with the <110> orientation includes at least 50% <110>;more preferably 75% <110>; even more preferably, the non-<110>orientations, individually, occur as less than 20% of the surfaceorientation. In another example, the surface can have a <200>orientation. Preferably, the aluminum or aluminum alloy with the <200>orientation includes at least 75%, 80%, 85%, 90%, 95%, or about 100%<200> surface orientation.

The aluminum or aluminum alloy can have a coarse grain or a fine grainsize (as determined by surface analysis). Preferably, the aluminum oraluminum alloy has a fine grain size. For example, the aluminum oraluminum alloy can have an average grain size of less than 500 μm, 400μm, 300 μm, 250 μm, 200 μm, 150 μm, or 100 μm. In one example, thealuminum or aluminum alloy has an average grain size of about 250 μm,200 μm, 150 μm, 100 μm, 75 μm, 50 μm, or 25 μm.

In one preferable example, the aluminum oxide layer is exposed to waterat a temperature of at least 85° C. That is, the process can includeforming a sealed, anodized-aluminum layer by a hot sealing process. Thehot sealing process includes exposing the anodized aluminum, preferably,a hard-anodized-aluminum layer, to water at a temperature of at least85° C., 90° C., 95° C., 98° C., 99° C., 100° C., or 101° C. In oneinstance, hard-anodized aluminum can be hot sealed in boiling or nearboiling water; in another instance the hard-anodized aluminum can besteam sealed. Preferably, anodized aluminum is hot sealed in boiling ornear boiling water. The water is preferably free of silicates andtransition metals (e.g., nickel), and/or other sealing additives. Thehot sealing of the hard-anodized-aluminum layer can include exposing thehard-anodized aluminum to hot water for at least 5 min/micron, 4min/micron, 3 min/micron, 2 min/micron, 1 min/micron, 30 sec/micron, or10 sec/micron. The process can, alternatively, include exposing a PVDalumina layer to water at a temperature of at least 85° C., 90° C., 95°C., 98° C., 99° C., 100° C., or 101° C. to form a hydrated PVD alumina.In one instance, the PVD alumina layer can be exposed to boiling or nearboiling water; in another instance the PVD alumina layer can be exposedto steam. Preferably, the PVD alumina layer is exposed to boiling ornear boiling water, where the water is free of silicates, transitionmetals, and/or sealing additives. Alternatively, a high hydroxyl contentaluminum oxide layer can be provided by PVD (e.g., PVD of aboehmite/bayerite layer). Preferably, the process includes formingaluminum hydroxides on exposed surface of the aluminum oxide layerduring the exposure of the materials to water at a temperature of atleast 85° C. Optionally, the process can include forming aluminumhydroxides within the aluminum oxide layer. More preferably, the processincludes forming a boehmite/bayerite region in the aluminum oxide layer.

The aluminum oxide layer (e.g., the sealed, anodized aluminum layer orthe hydrated PVD alumina layer) can have a thickness of about 1 μm toabout 50 μm. Specifically, the aluminum oxide layer can have a thicknessof less than about 50 microns, 40 microns, 30 microns, 25 microns, 20microns, 10 microns, 5 microns, 4 microns, 3 microns, 2 microns, 1micron, or 500 nm. Preferably, the aluminum oxide thickness is within arange of about 1 to about 30 microns, about 2 to about 25 microns, about3 to about 20 microns, or about 5 to about 25 microns. In one particularexample, the aluminum oxide layer has a thickness less than about 10microns.

In a specific example, the aluminum oxide layer is a sealed,anodized-aluminum layer which has a composition that is free ofsilicates, preferably, free of silicon and, more preferably, free ofnickel. For example, the sealed, anodized-aluminum layer can have acomposition that includes or consists of about 75 wt. % to about 85 wt.% Al₂O₃, about 3.5 wt. % to about 5.5 wt. % H₂O, and about 12.5 wt. % toabout 17.5 wt. % SO₃. In another specific example, the aluminum oxidelayer is a hydrated PVD alumina layer which has a composition thatincludes or, preferably, consists of aluminum, oxygen and hydrogen.

The process can then include coating the aluminum oxide layer with anaqueous silicate solution; that is, forming a coated, aluminum oxidelayer, where the aluminum oxide layer carries a layer/coating of anaqueous silicate solution. For example, the coated, aluminum oxide layercan be a coated, anodized-aluminum layer or a coated PVD alumina layer.In one particularly preferable example, the process includes applying anaqueous silicate solution to the sealed, anodized-aluminum layer.Alternatively, the process can include applying the aqueous silicatesolution to a hydrated PVD layer. Preferably, the aqueous silicatesolution is maintained at a temperature below 30° C., 25° C., or 20° C.

The coated aluminum oxide layer preferably includes or consists of thealuminum oxide layer (e.g., the sealed, anodized-aluminum layer) and asilicate solution layer. The silicate solution layer can have athickness of about 0.1 μm to about 5 μm, about 0.5 μm to about 4 μm, orabout 1 μm to about 3 μm.

The aqueous silicate solution has a pH of about 11 to about 13, about 11to about 12, or about 11 to about 11.5. Preferably, the aqueous silicatesolution has a composition that includes a ratio of SiO₂ to M₂O of about3.5 to about 2, about 3.5 to about 2.25, about 3.5 to about 2.5, about3.5 to about 2.75, or about 3.5 to about 3, where M is selected from Li,Na, K, and a mixture thereof. More preferably, the aqueous silicatesolution has a composition that includes a ratio of SiO₂ to B₂O₃ ofabout 10:1 to about 200:1.

In one instance, the coating process can include immersing the aluminumoxide layer in the aqueous silicate solution and then withdrawing thecoated, anodized-aluminum layer from the aqueous silicate solution. Inanother instance, the coating process can include spray coating or rollcoating the aluminum oxide layer with the aqueous silicate solution.

The coating process, preferably, excludes the formation ofaluminosilicates. More preferably, the process includes preventing theformation of an aluminosilicate. In one example, preventing theformation of aluminosilicate can include preventing the penetration ofthe aqueous silicate solution into aluminum oxide layer. Morepreferably, preventing the formation of the aluminosilicate includespreventing the dissolution of aluminum from the aluminum oxide layerinto the aqueous silicate solution. For example, the coating processprevents the diffusion of the silicate into the alumina and/or theinterdiffusion of the silicate and alumina thereby providing a productthat is free of an aluminosilicate or silicate/alumina interdiffusion.Processes for preventing the penetration of the aqueous silicatesolution into the aluminum oxide layer can include sealing pores in thealuminum oxide layer to reduce silicate solution penetration and therebyformation of interstitial Al/Si layers, providing a non-porous aluminumoxide layer, and/or rapidly drying the aqueous silicate solution toreduce or eliminate the mobility of the silicon atoms. Processes forpreventing the dissolution of aluminum from the aluminum oxide layerinto the aqueous silicate solution can include incompletely hydratingthe aluminum oxide layer or reducing the percentage of Al(OH)₃ in thealuminum oxide layer, conducting the coating process at a reducedtemperature (e.g., by chilling the aqueous silicate solution and/or thealuminum oxide layer), and/or rapidly drying the aqueous silicatesolution. In one example, the process can include preheating the coated,anodized-aluminum layer to a temperature of about 30° C. to about 100°C. immediately after the formation of the coated aluminum oxide layer.In another example, the process can include drying the coated,anodized-aluminum layer immediately after the formation of the coatedaluminum oxide layer. In another example, the process can includereducing a water content in the coated, anodized-aluminum layer by atleast 25%, 50%, or 75% immediately after the formation of the coatedaluminum oxide layer.

The process, preferably, further includes quickly applying the aqueoussilicate solution to the aluminum oxide layer after hot sealing (i.e.exposing the aluminum oxide layer to the hot water). For example, theprocess can include forming a coated, anodized-aluminum layer byapplying the aqueous silicate solution within 45, 40, 35, 30, 25, 20,15, 10 or 5 minutes of a conclusion of the hot sealing process. That is,the process can include immersing the sealed, anodized-aluminum layer inthe aqueous silicate solution; or spray coating or roll coating thesealed, anodized-aluminum layer with the aqueous silicate solutionwithin 45, 40, 35, 30, 25, 20, 15, 10 or 5 minutes of a conclusion ofthe hot sealing process. In another example, the process can includeforming a coating PVD alumina layer by applying the aqueous silicatesolution within 45, 40, 35, 30, 25, 20, 15, 10 or 5 minutes of removalfrom exposure to water at a temperature of at least 85° C.

Alternatively, the process can include holding or maintaining the hotsealed aluminum oxide layer in an atmosphere with a relative humidity ofat least 50%, 60%, 70%, 80%, 90%, or about 100% prior to coating thealuminum oxide layer with the aqueous silicate solution. For example, asealed, hard-anodized aluminum layer can be maintained in an atmospherewith a relative humidity of at least 50%, 60%, 70%, 80%, 90%, or about100% for a period longer than 45 min, 1 h, 2 h, 3 h, or 4 h, and thencoating with an aqueous silicate solution. In another example, theprocess can include holding or maintaining the hot water exposedaluminum oxide layer in water and then coating with an aqueous silicatesolution. Preferably, the aluminum oxide layer is held in water at atemperature of less than 75° C., 65° C., 60° C., 55° C., 50° C., 45° C.,40° C., 35° C., 30° C., 25° C., or 20° C. For example, the process caninclude holding, maintaining, or submerging the sealed,anodized-aluminum layer in water; and then forming the coated,anodized-aluminum layer by applying the aqueous silicate solution.

The coated, aluminum oxide layer includes an aqueous solution of analkali metal silicate carried on the surface of an aluminum oxide.Without being bound to theory, the dried, coated, aluminum oxide layercan include sufficient water to allow for the dissolution of the alkalimetal silicate from the aluminum oxide layer. That is, prior to apolymerization and curing step, the alkali metal silicate carried on thesurface of the aluminum oxide layer can be dissolved or removed from thesurface by, for example, washing the surface in water or an alkalisolution (e.g., 0.01 M^(aq) NaOH, or 0.1 M^(aq) NaOH).

An important step in the preparation of the coated/corrosion resistantproduct is the polymerization and curing of a silicate glass. Thesilicate glass can be formed from the heating and dehydration of anaqueous solution of an alkali metal silicate carried on the surface ofthe aluminum oxide layer. Alternative, the silicate glass can be formedby the infrared activation of the aqueous solution of alkali metalsilicate carried on the surface of the aluminum oxide layer.

In one example, the heating of the coated, aluminum oxide layerfacilitates the removal of water from the coating,dehydration-polymerization of SiO₄ groups, and the curing of thesilicate glass. For example, the process can include polymerizing andcuring a silicate glass by heating the coated, anodized-aluminum layerto a temperature of about 200° C. to about 500° C. The polymerizationand curing temperature can be in the range of about 200° C. to about500° C., preferably this temperature is about 200° C. to about 400° C.,about 250° C. to about 350° C., about 260° C. to about 325° C., or about260° C. to about 300° C. More preferably, the polymerizing and curing ofthe silicate glass includes heating the surface of the substrate, i.e.,the coated, anodized-aluminum layer, to a temperature of about 240° C.to about 320° C., about 260° C. to about 300° C., about 270° C. to about290° C., or about 280° C.

The polymerization and curing of the silicate glass preferably includesthe rapid heating and dehydration of the aqueous alkali metal silicate.Unexpectedly, the coated, aluminum oxide layer is resistant to thewell-known cracking and/or crazing of the surface caused by the rapidheating and/or dehydration of the aluminum oxide layer (see FIG. 7).Whereas aluminum oxide layers would crack, craze, or delaminate; thecoated, aluminum oxide layer can be heated to the polymerization andcuring temperature a rate of 1° C./s, 10° C./s, 25° C./s, 50° C./s, or100° C./s; or a rate of at least 10° C./s, 25° C./s, 50° C./s, or 100°C./s. Whereas visual identification of cracking, crazing, ordelamination is readily apparent, damages surfaces are mopre readilyidentifies by failure of the herein described test methods (e.g., the“pH 1 Test”, the “pH 14 Test”, or the “CASS Test”). In one preferableexample, the polymerization and curing of the silicate glass includesthe heating of the silicate layer (solution/glass) but incompleteheating of the underlying substrate.

The heating and dehydration of the aqueous silicate solution carried onthe surface of the aluminum oxide layer can be accomplished by, forexample, direct heating in an oven, heating by lamps, a vacuum process,or a combination thereof. In one preferable example, the coated,aluminum oxide layer is heated in an oven. In one instance, the coated,aluminum oxide layer is heated in a conventional oven. In anotherinstance, the coated, aluminum oxide layer is heated in a convectionoven that allows for the more rapid and even elevation of thetemperature of the coated, aluminum oxide layer. In yet anotherinstance, the coated, aluminum oxide layer is carried through a heatingzone (e.g., in a conveyor oven). Even more preferably, the coated,aluminum oxide is heated to the polymerization and curing temperature ata rate of at least 20° C./s, is heated for a heating time of less thanabout 30 min, and is then removed from the heat source to a temperatureof less than 50° C., 40° C., or 30° C., preferably removed from the heatsource to a temperature of about 20-25° C. (standard room temperatures).Preferably, the direct heating is for a heating time of less than about5 min, 10 min, 15 min, 20 min, 25 min, or 30 min. More preferably, theheating time is less than about 15 min.

In another example, the silicate glass can be formed by the infraredactivation of the alkali metal silicate layer carried on the surface ofthe aluminum oxide layer. For example, the coated, aluminum oxide layercan be polymerized and the silicate glass cured by exposing the coated,anodized-aluminum layer to an infrared (IR) source. In one instance, thecoated, aluminum oxide layer is exposed to IR heat lamps (e.g., shortwave or mid wave lamps). In another instance the coated, aluminum oxidelayer is carried through an IR exposure region (e.g., on a conveyor).The IR transmission from the IR source can be from about 1 to about 3 μm(short wave IR), from about 3 to about 5 μm (mid wave IR, orintermediate IR), or from about 2 to about 4 μm (IR-B). Preferably, theIR exposure is for an exposure time of less than about 15 seconds, 30seconds, 45 seconds, 60 second, 90 seconds, 120 seconds, 3 min, 4 min, 5min, or 10 min. More preferably, exposure time of less than about 15seconds, 30 seconds, 45 seconds, 60 second, 90 seconds, or 120 seconds.

Unexpectedly, the IR cured, silicate glass is resistant to thewell-known cracking and/or crazing of the surface. Whereas aluminumoxide layers crack, craze, or delaminate; the coated, aluminum oxidelayer can be exposed to the IR source and the resultant cured silicateglass appears as a uniform unbroken surface (see FIG. 7). Whereas visualidentification of cracking, crazing, or delamination is often visuallyapparent, damaged surfaces are more readily identified by failure of theherein described test methods (e.g., the “pH 1 Test”, the “pH 14 Test”,and/or the “CASS Test”). Herein, the products carrying the IR curedsilicate glass pass the “pH 1 Test”, the “pH 14 Test”, and the “CASSTest”.

In one specific example, the process of preparing a surface coating canconsist of forming a coated, anodized-aluminum layer by dip coating,spray coating, or roll coating a sealed, anodized-aluminum layer havinga thickness of about 1 μm to about 25 μm with an aqueous silicatesolution. The coated, anodized-aluminum layer can consist of the sealed,anodized-aluminum layer and a silicate solution layer, where thesilicate solution layer has a thickness of about 1 μm to about 3 μm, andthe sealed, anodized-aluminum layer has a composition that includesabout 75 wt. % to about 85 wt. % Al₂O₃, about 3.5 wt. % to about 5.5 wt.% H₂O, and about 12.5 wt. % to about 17.5 wt. % SO₃, and is free ofnickel and silicon. The process thereafter includes polymerizing andcuring the coated, anodized-aluminum layer to form a non-porous silicateglass, the polymerizing and curing includes heating the coated,anodized-aluminum layer to a temperature of about 225° C. to about 300°C. Wherein, the above described thickness, composition, and heatingfeatures can be further refined by the corresponding generaldisclosures.

In another specific example, the process can consist of hot sealing ananodized aluminum layer by exposing the anodized aluminum layer to waterat a temperature of at least 85° C., 95° C., or 100° C. The processthereafter includes either (A) forming a coated, anodized-aluminum layerby dip coating, spray coating, or roll coating the sealed,anodized-aluminum layer with an aqueous silicate solution within 20, 15,10 or 5 minutes of a conclusion of the hot sealing process, or (B)maintaining the sealed, anodized-aluminum layer in water after the hotsealing process and then forming the coated, anodized-aluminum layer bydip coating, spray coating, or roll coating with the aqueous silicatesolution. Herein, the sealed, anodized-aluminum layer has a thickness ofabout 1 μm to about 25 μm, the coated, anodized-aluminum layer consistsof the sealed, anodized-aluminum layer and a silicate solution layerthat has a thickness of about 1 μm to about 3 μm, and the sealed,anodized-aluminum layer has a composition that includes about 75 wt. %to about 85 wt. % Al₂O₃, about 3.5 wt. % to about 5.5 wt. % H₂O, andabout 12.5 wt. % to about 17.5 wt. % SO₃, and is free of nickel andsilicon. Thereafter, the process includes polymerizing and curing thecoated, anodized-aluminum layer to form a non-porous silicate glass, thepolymerizing and curing includes heating the coated, anodized-aluminumlayer to a temperature of about 225° C. to about 300° C. Wherein, theabove described thickness, composition, and heating features can befurther refined by the corresponding general disclosures.

In yet another specific example, the process of preparing a surfacecoating can consist of forming a coated, PVD alumina layer by dipcoating, spray coating, or roll coating a PVD alumina layer having athickness of about 1 μm to about 25 μm with an aqueous silicatesolution. The coated, PVD alumina layer can consist of the PVD aluminalayer and a silicate solution layer, where the silicate solution layerhas a thickness of about 1 μm to about 3 μm. The process thereafterincludes polymerizing and curing the coated, PVD alumina layer to form anon-porous silicate glass, the polymerizing and curing includes heatingthe coated, PVD alumina layer to a temperature of about 225° C. to about300° C. Wherein, the above described thickness, composition, and heatingfeatures can be further refined by the corresponding generaldisclosures.

EXAMPLES

By way of example and not limitation, test samples, prepared as follows,are illustrative of various embodiments of the present disclosure andfurther illustrate experimental testing conducted.

The herein described aqueous silicate solution can be analkali-borosilicate solution containing a mixture of sodium and lithiummetal counterions. The alkali-borosilicte solution can be prepared bycombining concentrated, commercial, liquid sodium silicate and lithiumsilicate solutions. Then adding to this lithium-sodium solution a boraxsolution (sodium tetraborate decahydrate (Na₂B₄O₇.10H₂O) in water). Thefinal borax concentration in the coating solution can be between 1-5% byweight. In one example, the aqueous silicate solution contains 13.0%SiO₂, 1.7% Na₂O, 1.2% Li₂O, 1.1% B₂O₃, and 83.0% H₂O by weight, had aspecific gravity of about 1.15. Prior to use, the solution was filteredthrough a 1.2 mm filter. The aqueous silicate solution has a specificgravity of 1.136 and was held at 20° C.

The following general procedures were used to produce test samples:

Anodization: Component testing was conducted on automotive-trim testforms which were produced by extruding and heat treating a 6061 seriesaluminum alloy. The test forms were approximately 100 mm by 500 mm andincluded a multitier cross-sectional profile. The aluminum form wasdegreases (alkaline), desmutted (nitric acid), and then anodized in asulfuric acid bath at 19° C., for 15 min, at 16V and 1.5 A/dm². Theanodized sample was then rinsed three times with DI water. This yieldedan unsealed, anodized-aluminum layer carried on the aluminum form.

Hot Sealing: following anodization and unless otherwise noted, testsamples were hot sealed at about 97° C. following standard industrialprocedures. A test standard was established with a hot sealing time of 2minutes per micron of anodization (e.g., 20 minutes for a 10 micronthick anodized layer).

Coating: test samples (hot sealed or not) were coated with aqueoussilicate solution by immersion, spray coating, or roll coating toprovide a coating thickness of about 1 μm to about 5 μm. Preferably,test samples were immersed in the aqueous silicate solution for fiveminutes. Unless otherwise noted the aqueous silicate solution was theabove described alkali-borosilicate solution.

Polymerizing and Curing: coated test samples were subjected to elevatedtemperatures to polymerize and cure the silicate coatings. Thetemperatures can be applied by standard, convection, or IR oven. Thecuring times (time subjected to elevated temperatures) ranged from about3 to 30 minutes. No benefit was incurred by heating beyond 30 minutes.

Test samples were subjected to the following testing: a 24 hour CASStest, a 2 minutes pH 14 test, a fogging test, and an abrasion test.Table 1 provides data on the preparation of prior art comparativesamples:

Sample Anodize to Coating Curing Number Seal Coat Time Type Time¹ Ref.C1 None 0 ABS²  3 min Jennings³ C2 None 0 ABS²  7 min Jennings³ C3 None0 ABS² 15 min Jennings³ C4 None 0 ABS² 30 min Jennings³ C5 800 sec Cold 0 0.5 wt. % 0 Lawlor⁴ then 800 sec sodium Hot silicate ¹Time at acuring temperature of 280° C. ²The above described alkali-borosilicatesolution. ³U.S. Pat. No. 8,173,221 ⁴U.S. Pat. No. 7,851,025

Table 2 provides data on the preparation of comparative samples that canbe viewed as amendments on the prior art:

Sample Anodize to Coating Curing Number Seal Coat Time Type Time¹ Ref.C6 None  5 h ABS² 15 min Jennings³ C7 None 24 h ABS² 15 min Jennings³ C8800 sec Cold 0 ABS² 15 min Lawlor⁴ then 800 sec Hot ¹Time at a curingtemperature of 280° C. ²The above described alkali-borosilicatesolution. ³U.S. Pat. No. 8,173,221 ⁴U.S. Pat. No. 7,851,025

Table 3 provides data on the preparation of herein disclosed samplesusing the above described alkali-borosilicate solution:

Sample Hot Seal¹ Seal to Coat Time² Curing Time³ 1 0.5 0 15 2 2 0 15 3 60 15 4 2  5⁴ 15 5 2 24⁴  15 6 2  5⁵ 15 7 2 24⁵  15 8 2 0 3 9 2 0 7 10 20 30 ¹Hot seal time in minutes per micron of anodized layer thickness.²The time in hours between hot sealing and coating with thealkali-borosilicate solution. ³Time at a curing temperature of 280° C.⁴Samples were maintained in air at room temperature for the time betweenhot sealing and coating. ⁵Samples were maintained in water at roomtemperature for the time between hot sealing and coating.

Table 4 provides test results for all samples.

Sample 24 hour 2 min Number CASS pH 14 Fogging Abrasion C1 F P(0) F P(0)C2 F P(+) F P(0) C3 F P(+) P(0) P(0) C4 F P(+) P(+) P(0) C5 F F F F C6 FP(0) P(0) P(0) C7 F P(0) P(0) P(0) C8 F P(+) F P(0) 1 P(+) P(+) P(+)P(+) 2 P(+) P(+) P(+) P(+) 3 P(0) P(0) P(+) P(+) 4 P(0) F P(0) P(0) 5P(0) F P(0) P(0) 6 P(0) P(0) P(0) F 7 P(0) P(0) P(0) F 8 P(+) P(0) FP(0) 9 P(0) P(+) P(0) P(0) 10  P(+) P(+) P(+) P(+)

TOF-SIMS testing: Comparative Sample 3 (unsealed) and Sample 2 (sealed)were ion milled and compositional analysis was completed bytime-of-flight secondary ion mass spectroscopy (TOF-SIMS). Millingdistances were approximately 1 micron per cycle. Table 5 provides atomicpercentages of Silicon and Aluminum (balance Oxygen):

Comparative Sample C3 Sample 2 Milling Cycle Si Al Si Al 1 29.4 0.9 30.01.4 2 28.6 0.1 29.3 0.1 3 28.5 0.1 29.3 0.2 4 28.3 0.0 3.2 29.3 5 28.70.2 0.0 34.0 6 1.4 31.7 0.0 33.8 7 1.3 32.9 0.0 34.2 8 0.6 32.7 0.0 34.39 0.4 33.2 0.0 34.9 10 0.4 33.1 0.0 34.4 11 0.8 33.3 0.0 34.8 12 1.032.7 0.0 34.9 13 0.6 33.0 0.0 34.7 14 0.4 33.7 0.0 90 15 0.5 33.2 0.0100 16 0.5 37.9 0.0 100 17 0.0 99.5 0.0 99.7 18 0.0 99.8 0.0 100

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

What is claimed:
 1. A process for preparing a silicate surface coatingcomprising: forming a coated-aluminum-oxide layer by applying an aqueoussilicate solution to an aluminum oxide layer that has a thickness ofabout 1 μm to about 25 μm, the aluminum oxide layer consisting of asealed, anodized-aluminum layer or a hydrated PVD alumina layer andhaving an EDX composition that is free of silicon, boron and/or nickel,the aqueous silicate solution having a pH of about 11 to about 13, acomposition that includes a ratio of SiO₂ to M₂O of about 3.5 to about2, where M is selected from Li, Na, K, and a mixture thereof, and aratio of SiO₂ to B₂O₃ of about 10:1 to about 200:1; and thereafter,polymerizing and curing a silicate glass on the sealed,anodized-aluminum layer by (A) heating the coated, anodized-aluminumlayer to a temperature of about 200° C. to about 500° C. or (B) exposingthe coated, anodized-aluminum layer to an infrared source.
 2. Theprocess of claim 1 further comprising: providing an aluminum surface;anodizing the aluminum surface to provide an unsealed, anodized-aluminumlayer; and then hot sealing the unsealed aluminum oxide layer to providethe sealed, anodized-aluminum layer.
 3. The process of claim 2 furthercomprising a hot sealing time of less than 6 min/micron.
 4. The processof claim 3, wherein the hot sealing time is less than 5 min/micron. 5.The process of claim 4, wherein the hot sealing time is less than 2min/micron.
 6. The process of claim 5, wherein the hot sealing time isless than 2 min/micron.
 7. The process of claim 2 further comprising hotsealing the unsealed anodized-aluminum layer and the forming the coated,anodized-aluminum layer within less than 60 minutes.
 8. The process ofclaim 7, where the coated, anodized-aluminum layer is formed within lessthan 30 minutes of the hot sealing.
 9. The process of claim 8, where thecoated, anodized-aluminum layer is formed within less than 10 minutes ofthe hot sealing.
 10. The process of claim 2 further comprising holdingthe sealed, anodized-aluminum layer in a wet atmosphere, in water, orcoated with water; and then forming the coated, anodized-aluminum layerby applying the aqueous silicate solution.
 11. A process for preparing asilicate surface coating comprising: hot sealing an anodized aluminumlayer for less than 6 minutes/micron of a thickness of the anodizedaluminum layer; then within 30 minutes of a completion of the hotsealing immersing the hot sealed anodized aluminum layer in an aqueoussilicate solution for about 5 minutes, the aqueous silicate solutionhaving a pH of about 11 to about 13, a composition that includes a ratioof SiO₂ to M₂O of about 3.5 to about 2, where M is selected from Li, Na,K, and a mixture thereof, and a ratio of SiO₂ to B₂O₃ of about 10:1 toabout 200:1; and then without rinsing, polymerizing and curing theaqueous silicate solution coated, hot sealed anodized aluminum layer by(A) heating the coated, anodized-aluminum layer to a temperature ofabout 200° C. to about 500° C. and/or (B) exposing the coated,anodized-aluminum layer to an infrared source.
 12. The process of claim11, wherein the hot sealed anodized aluminum layer has an EDXcomposition that is free of silicon, boron, and/or nickel.
 13. Theprocess of claim 11, wherein the hot sealed anodized aluminum layer hasan EDX composition that consists of aluminum, oxygen, sulfur, and anoptional colorant.
 14. The process of claim 11, wherein the silicatesurface coating includes an aluminum oxide layer having a compositionthat is free of silicates; and a silicate glass layer carried directlyon the aluminum oxide layer and having a silicate glass layer EDXcomposition that consists of silicon, oxygen, sodium, optionallylithium, and optionally boron; wherein the silicate glass layer EDXcomposition is free of aluminum.